Holy crap was that fast! Kudos to you! And I totally dig your headphone stand!
Best,
Anand.
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Thanks! I'll have to work on my impulse control.
Why do that?
Love your work. Impressive.
Inspirational too. I'll have to warm up the iron.
Don't short the input cap! It's funny now, but I had 5 minutes of ACP+ excitement yesterday: I thought I would bypass (short out) the Elna RFS electrolytic 10uF input cap since I already had a big film cap in the output of my CD player. Nope, NO SOUND! Removed shorting link, and ACP+ was back to working fine. Plugged in sacrificial headphones and tried shorting it again while switched on, and sound went out with a pop, but came right back when short removed.
So, ACP+ depends on some kind of input cap. I'd like it to be a film cap, and I noticed the prototype ACP+ had "3uF" silk screened on the pcb. What is the smallest input cap one can get away with here?
So, ACP+ depends on some kind of input cap. I'd like it to be a film cap, and I noticed the prototype ACP+ had "3uF" silk screened on the pcb. What is the smallest input cap one can get away with here?
I got so excited about this amp decided to buy another pair of headphones, Sennheiser 58X.
They seem like a great deal and they’re open back which is what I actually prefer but don’t have.
My current headphones are closed back planar magnetic oppo’s (no longer made), the closed back being better suited for use in noisy or public spaces.
Anyway, the headphones appear to be a cross between a HD600 and HD660S at a much reduced price.
We’ll see how they compare with the oppo’s.
They seem like a great deal and they’re open back which is what I actually prefer but don’t have.
My current headphones are closed back planar magnetic oppo’s (no longer made), the closed back being better suited for use in noisy or public spaces.
Anyway, the headphones appear to be a cross between a HD600 and HD660S at a much reduced price.
We’ll see how they compare with the oppo’s.
Well you have half the supply voltage at the gate of input jet, so having a cap at the input is important.
Yeah don’t do that because it will short the input to low, I know because in the rush to build mine I reversed the input caps. During the voltage checks I measured the power supply drawing 400mA instead of 300mA, and the FETs weren’t biased correctly. As soon as I corrected it the amp worked just fine.
By the way I made an adapter to connect my speakers to the TRS output and I can tell you that it drives my (90dBSPL/W) JBL L100T3s quite nicely, loud enough to wake the kids and neighbors if you’re not careful. It’s a beautiful sounding amp, now I want a J2 even more!
By the way I made an adapter to connect my speakers to the TRS output and I can tell you that it drives my (90dBSPL/W) JBL L100T3s quite nicely, loud enough to wake the kids and neighbors if you’re not careful. It’s a beautiful sounding amp, now I want a J2 even more!
I bet there was also a bleed resistor draining the Big Film Cap. So yeah- the guts of ACP are supposed to bias-hald-way up the supply voltage, you slammed it to the floor (zero V), it can't be happy. You NEED a C1.
> What is the smallest input cap
The stock input R is 75k. Reactance chart tells us that a 0.1uFd against 75k is 22Hz, which is rather high for "high"-fidelity (-1dB @ 44Hz, so shaves deep bass). That's not considering the value of the BFC in the CD box, or all the bass-cuts from the studio microphone to the ACP.
1uFd would be 2.2Hz, little effect on music, but is a pretty big film cap for me. (Some folks don't mind the size and expense.)
A half-mike might be a happy compromise.
The cap has sure bias, so an electro works fine, and 1uFd is very cheap in electrolytic, but electros distort near cut-off.
What works WELL for many designers is to pick the electro about 100X bigger than needed for bass response. This ensures the AC/Audio voltage across the cap is super-small, so nothing to distort. All your (older) music came through hundreds of very large electros. If we assume recordings don't have much under 50Hz (few do) and 0.1uFd is just OK, then 10uFd (100X bigger) should be "inaudible". (Yes, I know: you saw it, you will still hear it.)
I think Mr Pass knows a LOT about musical sound. Not only for his $13,000 products, but also what works above its price-point.
There is a different HACK. Modify the known-good circuit. Your own risk.
The JFET can bias with a large resistor. Using 1Meg a 0.01uFd cap is almost good enough.
Lift the Gate leg of Q1 and bend it up. Lift the "-" leg of C1, turn and bend it up. Get a 1Meg resistor and some small wire. Re-rig it as shown, air-wired. New cap "C13", look in your 0.1u box; if you have a 0.05u or 0.27u which looks sweet, use what you like.
However ALL the sound to the headphones has to go through C3. And the flaws in any headphone overwhelm the flaws of even an electrolytic cap. We may be lipsticking the wrong end of the pig.
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> Lift the Gate leg of Q1 and bend it up. Lift the "-" leg of C1, turn and bend it up. Get a 1Meg resistor and some small wire. Re-rig it as shown, air-wired. New cap "C13", look in your 0.1u box; if you have a 0.05u or 0.27u which looks sweet, use what you like.
Really bad idea.
If you want to make a low noise Gnd reference for the LTP, you are only doing it half way.
Patrick
Really bad idea.
If you want to make a low noise Gnd reference for the LTP, you are only doing it half way.
Patrick
I was one of the lucky builders at the BAF event. A big thank you to Nelson Pass and all the people who help to make the workshop happen. Your generosity is greatly appreciated.
I decided to put mine in an enclosure. I bought a cheap $20 case on eBay and didn't really like the way it looked after I received it, especially the finish on the aluminum. Still, it makes the ACP+ more useable for me.
I decided to put mine in an enclosure. I bought a cheap $20 case on eBay and didn't really like the way it looked after I received it, especially the finish on the aluminum. Still, it makes the ACP+ more useable for me.
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Nice, you are a really lucky one who can meet our other diy friends!
From germany would it be a long trip, but hey ZM has it also done so why should i do it not also? Mmmh ..... My government (wife) would say something like "You're out of your mind".
One day i will see Frisco. ;-) Have fun!
From germany would it be a long trip, but hey ZM has it also done so why should i do it not also? Mmmh ..... My government (wife) would say something like "You're out of your mind".
One day i will see Frisco. ;-) Have fun!
Looks good!
It will also supres noise.
How did you get the holes in the front panel at the exact positions?
I used digital calipers to measure the positions and put the locations into "Front Panel Designer" in case I wanted to make a nicer version. I've attached the file. If you use it, drill the holes a little bigger. The sizes are exactly the size of the shafts, you will need a little leeway to get it to fit.
Thank you very much.
Is it for this software package?
Front Panel Express: Front Panel Design Software and CAD Conversion Service: Home
Is it for this software package?
Front Panel Express: Front Panel Design Software and CAD Conversion Service: Home
